Objective To compare the effect of evidence based information on risk with that of standard information on informed choice in screening for colorectal cancer.Design Randomised controlled trial with 6 months’ follow-up.Setting German statutory health insurance scheme.Participants 1577 insured people who were members of the target group for colorectal cancer screening (age 50-75, no history of colorectal cancer).Interventions Brochure with evidence based risk information on colorectal cancer screening and two optional interactive internet modules on risk and diagnostic tests; official information leaflet of the German colorectal cancer screening programme (control).Main outcome measure The primary end point was “informed choice,” comprising “knowledge,” “attitude,” and “combination of actual and planned uptake.” Secondary outcomes were “knowledge” and “combination of actual and planned uptake.” Knowledge and attitude were assessed after 6 weeks and combination of actual and planned uptake of screening after 6 months.Results The response rate for return of both questionnaires was 92.4% (n=1457). 345/785 (44.0%) participants in the intervention group made an informed choice, compared with 101/792 (12.8%) in the control group (difference 31.2%, 99% confidence interval 25.7% to 36.7%; P<0.001). More intervention group participants had “good knowledge” (59.6% (n=468) v 16.2% (128); difference 43.5%, 37.8% to 49.1%; P<0.001). A “positive attitude” towards colorectal screening prevailed in both groups but was significantly lower in the intervention group (93.4% (733) v 96.5% (764); difference −3.1%, −5.9% to −0.3%; P<0.01). The intervention had no effect on the combination of actual and planned uptake (72.4% (568) v 72.9% (577); P=0.87).Conclusions Evidence based risk information on colorectal cancer screening increased informed choices and improved knowledge, with little change in attitudes. The intervention did not affect the combination of actual and planned uptake of screening.Trial registration Current Controlled Trials ISRCTN47105521.